In the prior art, a sheet cutting machine conveys sheets one by one along a conveying path, cuts each of the sheets into margins and desired size of products, removes the margins from the conveying path, and thereby stacks only the products on a tray. The sheet cutting machine, for example, comprises a slitting unit arranged to cut the sheet in a conveying direction using slitters, and a cutting unit arranged downstream of the slitting unit to cut the sheet in a direction perpendicular to the conveying direction using a pair of cutting blades.
The cutting unit includes a pair of upstream conveying rollers to convey the sheet along the conveying path, a pair of cutting blades arranged downstream of the upstream conveying rollers to cut the sheet into the products and the margins, and a pair of downstream conveying rollers arranged downstream of the cutting blades to convey along the conveying path the products cut off from the sheet.
In order to separate a margin of the sheet front end from the sheet and remove the margin from the conveying path, the cutting unit first conveys the sheet using the upstream conveying rollers in such a manner that the sheet is travelled from a gap between the pair of the cutting blades by a predetermined length. The cutting unit then cuts the sheet in the direction perpendicular to the conveying direction using the pair of the cutting blades. Thereby, the margin of the sheet front end is separated from the sheet and removed from the conveying path by falling down from a gap between the cutting blades and the downstream conveying rollers.
However, when the length in the conveying direction of the margin is longer than a distance between the cutting blades and the downstream conveying rollers, it is impossible to remove the margin from the conveying path in one cutting operation described above. This is because the sheet is received by the downstream conveying rollers when being conveyed by the upstream conveying rollers, and as a result, the margin which has been cut off from the sheet is conveyed along the conveying path by the downstream conveying rollers.
Each of Patent Literatures 1 and 2 discloses a sheet cutting machine which can solve such a problem. In the sheet cutting machines of Patent Literatures 1 and 2, when the length in the conveying direction of the margin is equal to or longer than a distance between the cutting blades and the downstream conveying rollers, the margin is cuts off in several cutting operations instead of one cutting operation described above.
Conveyance of the sheet by the upstream conveying rollers needs to be temporarily paused while the sheet is cut. In other words, in order to separate the margin from the sheet in the several cutting operations described above, conveyance of the sheet has to be paused during every cutting operation. This reduces the efficiency of the sheet cutting machine.